One estimate suggested a policy change could cause as many as 100,000 to 350,000 Scouts to leave. And it could also affect donors - just more than half of local councils reported to BSA that their donors supported the current ban.

Of the more than 100,000 Scouting units in the U.S., 70 percent are chartered by religious institutions. While these sponsors include liberal churches opposed to any ban on gays, some of the largest sponsors are relatively conservative denominations that have previously supported the broad ban - notably the Roman Catholic Church, the Church of Jesus Christ of Latter-day Saints and Southern Baptist churches.

The Church of Jesus Christ of Latter-day Saints announced in April that it supports the new proposal. Leaders of some smaller, conservative denominations have opposed it.

"Ultimately we can't anticipate how people will vote but we do know that the result will not match everyone's personal preference," said Deron Smith, BSA's national spokesman.